BK Butler Audio is a vacuum tube audio company founded by Brent K. Butler, based in Denver, Colorado. Butler began developing tube-based overdrive circuits in the mid-1970s, initially inspired by the sound of Hammond organ through tube amplification. In 1979 he released his first official Tube Driver under the Butronics name, and the iconic 4-knob Tube Driver circuit was designed in 1983. Through the 1980s the pedals were distributed through Chandler Industries, and Butler later ran Tube Works before reclaiming the TubeDriver trademark in 2000.

The company is best known for the hand-built Tube Driver, a 12AX7-powered overdrive pedal that has become a sought-after piece of gear among guitarists for its warm, dynamic tube saturation. Butler personally builds and signs each unit from his Colorado workshop, offering both the standard 4-knob version and a 5-knob "Real Deal" model with a bias control. Other trademarks in the Butler Audio family include TubeDriver BLUE, Thermionic, MosValve, and Blue Tube.

Beyond guitar effects, Butler Audio has expanded into consumer audio with tube-hybrid amplification products, including the TDB-series car audio amplifiers, TDB home theater amplifiers, and the MONAD A100 Class-A monoblock. The Tube Driver circuit has a long association with players such as Eric Johnson, David Gilmour, and Billy Gibbons, who helped cement its reputation as a tube overdrive standard.

BK Butler Audio has 2 products cataloged on Equipboard, including Overdrive Effects Pedals. Their gear is featured by 14 artists, with the strongest followings in Rock, Pop, and Folk, World, & Country. Notable users include David Gilmour, J Mascis, and Eric Johnson.